A powerful neuroscience tool is available to investigate brain development, mechanisms of memory and learning, and brain dysregulation in neuropsychiatric diseases like addiction, depression, schizophrenia and Alzheimer’s disease. This molecular biology tool can selectively and robustly turn on genes in vitro and in brain neurons of living adult rats. It can turn on a single gene or multiple genes at the same time, and it can control the amount of increased gene expression.